Vertical (Height) Reference System

Vertical or height reference systems define geographic elevation and depth in relation to sea level.

The current height reference system in British Columbia is based on the Canadian Geodetic Vertical Datum of 1928 (CGVD28) which was adopted in 1935. Canada is introducing a new datum known as the Canadian Geodetic Vertical Datum of 2013 (CGVD2013).

Canadian Height Modernization Initiative

Historically, the definition of this height reference system was separate from the definition of the horizontal reference system. With the implementation of the Canadian Spatial Reference System, this is changing.

It will be realized primarily through the use of an accurate Canada-wide geoid model, CGG2013. This will allow users to determine accurate elevations anywhere in Canada.

Implementation

The implementation of CGVD2013 is in progress. Natural Resources Canada has completed a readjustment of stable and accurate benchmarks across Canada at a spacing of approximately 500 km.

The new datum will result in changes in benchmark elevations across B.C. The new primary vertical benchmark heights will differ from the current published heights from a few centimetres to 50 cm, depending on the area of the province. Approximate shifts at various locations across the province:

The expected relative accuracy of elevations determined using CGG2013 is approximately 2 cm for points separated by up to 100 km, even in the Rocky Mountains area of B.C.

The new datum will be accessible directly through space-based positioning tools like GPS, as well as through monument networks including:

• Federal & provincial active control points
• Canadian Base Network
• Provincial High Precision Network

Both traditional and space-based techniques will co-exist throughout the transition period.

Transition

In order to ease transition to the modern vertical datum, the Provincial Government will take steps to:

• Provide support tools that enable height determination to facilitate adoption among user communities
• Introduce a set of transformation parameters and corresponding software tools to support conversion of existing data sets referenced to CGVD28
• Disseminate information on heights of existing federal and provincial benchmarks using the new datum
• Incorporate existing infrastructure of benchmarks into new system to minimize disruption to stakeholders and maximize access

The CGVD28 datum will continue to co-exist with CGVD2013 in the near future.

Stakeholder Consultation

Stakeholders must be consulted to ensure the envisioned modernization and related transition is conducted in a manner that minimizes negative impacts to business and users, while maximising benefits to all concerned. More information on vertical modernization for B.C. stakeholders and clients:

• Canadian Height Modernization Stakeholders' Information Paper (PDF)